Phase alignment determines whether sounds sum by amplitude or by power

Evidence

Sound sources are coherent if they or their partials have the same frequencies. Depending on their phase difference they can: • add constructively if they have the same phase; • add destructively if they are in opposite phase; or • in other cases the result depends on the amplitudes and phases of the components. 2. Sound sources are incoherent if their frequencies do not coincide, in which case the powers of the signals are summed. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 216

Categorization

• DEFINE: Defines coherent vs. incoherent sound sources — the core distinction governing all sound-field superposition.